The invention relates to a process for transferring heat from fluid mixtures containing a polymerizable monomer and an active polymerization catalyst.
The invention also relates to a process for the polymerization of a polymerizable monomer in live polymer dispersions and to an installation for conducting polymerization reactions involving the cooling of live polymer dispersions.
In particular, the invention relates to the transfer of heat from mixtures contained from suspension-polymerization of alkenes containing monomer and active catalyst particles.
It is already known and usual to transfer reaction heat from the live polymer dispersion formed during the polymerization of a monomer such as, for example, a 1-alkene. For instance, this may be done by cooling by heat-exchange through the reactor wall, by evaporating the excess or unreacted monomer and/or by employing a dispersing agent. However, the amount of heat which can reasonably and economically be transferred is limited since the heat exchange area of the reactor wall and surface area for monomer evaporation are limited and increasing these areas is achieved only at almost prohibitively high costs.
Heat can be transferred from a live polymer dispersion with external cooling by removing the live polymer dispersion from the reactor or other containing vessel and circulating the dispersion through an external cooler and then feeding the thus cooled dispersion back to the reactor vessel as described in U.S. Pat. No. 2,984,657. In this way, the heat exchange area no longer depends on the size and configuration of the reaction vessel. If desired, this area may therefore be extended to permit more heat transfer. However, a major problem arises from caking in the external cooler resulting from the continued polymerization in the live dispersion during its passage through the external cooler. This caking or incrustation results in increased flow resistance to the passage of the live dispersion through the cooler and a decreased heat-exchanging capacity. Consequently, long before the cooler becomes useless it has to be discarded because the caking clogs up the external cooler. This caking problem becomes more serious the smaller the channel diameter is in the external cooler through which the live dispersion must pass. This already known process attempts to overcome the caking problem by creating conditions of laminar flow, characterized by Reynolds Numbers maximall 2000, in the external cooler outside the reaction vessel because no polymerization is said to take place in such a flow range. However, this laminar flow removes or exchanges less heat than a turbulent flow thereby significantly reducing the effectiveness of the external cooler.
The invention aims at meeting the need for a means for transferring heat from a live polymer dispersion without limitations on the amount of heat to be transferred, and without caking or incrustation problems.
The present invention makes it possible to very effectively transfer heat, independent of the reaction vessel geometry, from a live polymer dispersion using equipment occupying little space while effectively overcoming the caking problem.